Labor successfully referred the commitment to the upper house's economics committee on Monday, with a report due the day before the budget is to be handed down on May 8.

The inquiry will look at the companies' wage growth and employment estimates, while also asking them to detail how much tax they have paid in the past five years and the expected tax benefit if the cuts are enacted.

The government is yet to get the Senate's support for its legislation to cut the corporate tax rate from 30 per cent to 25 per cent.

Debate on the bill was postponed on Monday as the government continues to lobby for the crucial votes of independents Derryn Hinch and Tim Storer.